Historically, the pneumatic tire has been fabricated as a laminate structure of generally toroidal shape having beads, a tread, belt reinforcement, and a carcass. The tire is made of rubber, fabric, and steel. The manufacturing technologies employed for the most part involved assembling the many tire components from flat strips or sheets of material. Each component is placed on a building drum and cut to length such that the ends of the component meet or overlap creating a splice.
In the first stage of assembly the prior art carcass will normally include one or more plies, and a pair of sidewalls, a pair of apexes, an innerliner (for a tubeless tire), a pair of chafers and perhaps a pair of gum shoulder strips. Annular bead cores can be added during this first stage of tire building and the plies can be turned around the bead cores to form the ply turnups. Additional components may be used or even replace some of those mentioned above.
This intermediate article of manufacture would be cylindrically formed at this point in the first stage of assembly. The cylindrical carcass is then expanded into a toroidal shape after completion of the first stage of tire building. Reinforcing belts and the tread are added to this intermediate article during a second stage of tire manufacture, which can occur using the same building drum or work station.
This form of manufacturing a tire from flat components that are then formed toroidally limits the ability of the tire to be produced in a most uniform fashion. As a result, an improved method and apparatus has been proposed, the method involving applying an elastomeric layer on a toroidal surface and placing and stitching one or more cords in continuous lengths onto the elastomeric layer in predetermined cord paths. The method further includes dispensing the one or more cords from spools and guiding the cord in a predetermined path as the cord is being dispensed. Preferably, each cord, pre-coated with rubber or not so coated, is held against the elastomeric layer after the cord is placed and stitched and then indexing the cord path to a next circumferential location forming a loop end by reversing the direction of the cord and releasing the held cord after the loop end is formed and the cord path direction is reversed. Preferably, the indexing of the toroidal surface establishes the cord pitch uniformly in discrete angular spacing at specific diameters.
The above method is performed using an apparatus for forming an annular toroidally shaped cord reinforced ply which has a toroidal mandrel, a cord dispenser, a device to guide the dispensed cords along predetermined paths, a device to place an elastomeric layer on the toroidal mandrel, a device to stitch the cords onto the elastomeric layer, and a device to hold the cords while loop ends are formed. The device to stitch the cords onto the elastomeric layer includes a bi-directional tooling head mounted to a tooling arm. A pair of roller members is mounted side by side at a remote end of the tooling head and defining a cord exiting opening therebetween. The arm moves the head across the curvature of a tire carcass built on a drum or core while the cord is fed through the exit opening between the rollers. The rollers stitch the cord against the annular surface as the cord is laid back and forth across the surface, the first roller engaging the cord along a first directional path and the second roller engaging the cord in a reversed opposite second directional path.
The toroidal mandrel is preferably rotatable about its axis and a means for rotating is provided which permits the mandrel to index circumferentially as the cord is placed in a predetermined cord path. The guide device preferably includes a multi axis robotic computer controlled system and a ply mechanism to permit the cord path to follow the contour of the mandrel including the concave and convex profiles.
While working well, certain challenges exist in the aforementioned proposed apparatus and method. For example, it would be desirable for the tooling head to maintain a constant optimal pressure against the annular surface. Excessive pressure can damage the cord or the underlying layer, resulting in a less than satisfactory cord layer in the finished tire. Excessive pressure can also break the cord, requiring a re-application of the cord layer and consequently detrimentally increasing manufacturing times. On the other hand, too little pressure on the cord may result in a less than optimal adherence of the cord to the underlying layer. Less than a proper level of adherence between the cord and the underlying layer may allow the cord to shift out of position during or after the cord laying procedure, resulting again in a cord layer that is defective in the finished tire.
Existing tooling heads, however, have proven less than adequate in maintaining constant optimal pressure against the annular core surface. Imperfections in the previously applied layers and the fixed spatial disposition of the rollers relative to the core surface result in a variable contact pressure exerted by the rollers against the annular surface. The consequence is a less controlled application of the cord against the annular surface.
A further drawback in proposed bi-directional tooling heads for laying a single end cord against an annular core surface is that such tooling heads are undesirably complicated and expensive to build and maintain. Such heads incorporate mechanical fingers and paddles to loop and pressure the cord into the ply compound as the head traverses the core surface. Controlling the pressure that such mechanisms exert upon the cord and annular surface, however, has proven problematic in view of the complexity of the mechanism itself and surface anomalies in the previously applied layer(s).
A need, accordingly, remains for an applicator head that is simple to construct, operationally reliable and efficient, and effective in bi-directional application of a single end cord to a tire carcass. Furthermore, a need exists for an applicator head that can effectively apply a tire cord at a constant optimal pressure against an annular core surface in order to adjust for surface layer(s) anomalies and thickness.